I suspect this is why younger entrepreneurs tend to build bigger companies, but have a lower chance of success. The size of an eventual company comes from the size of the market it's serving. Basic needs - food, socializing, sex, information, transportation - are shared by nearly everyone, and so the markets are huge. But everyone can see any problems that arise in those areas, and so the competition to win the market is intense.
Building something like software for petroleum geologists working in undersea basins is a much tinier market, but many fewer people have the requisite domain knowledge to even understand what the problems are. So your chances of success are higher, but you aren't going to strike it big like Facebook.
Even better startups come from deep business knowledge. Not necessarily unicorns, but great lifestyle and niche businesses that make the founders rich. And really, do you need to buy two Lear jets?
There's always been silly startup ideas, but that's mainly because a lot of people are silly. The "playing house" thing seems to be a different phenomenon: over the last few years I came across people who were very smart, very driven, but completely focused on other people's opinions. They like winning contests and climbing ladders. Now that startups are becoming a respectable career path, more and more of these people are trying to start startups.
In the corporate world, you can always focus on the next presentation, the next interview, the next hurdle, and gradually iterate upwards. To build a company you need to think in terms of fundamentals, to think long-term, and to think independently: members of this type can be very good at producing polished and sensible-sounding market analyses but distinctly bad at those three.
Of course a bunch of twenty somethings gravitate repeatedly to social apps; one of the core focuses of their lives to that point, whether they know it or not, is to learn how to be a social creature.
As you get older and more experienced, you start to unearth the "real" problems in the world oftentimes in some niche you could have never predicted you'd be involved in your younger years.
I could be completely wrong, just something I've always pondered when seeing so many of these ridiculous startups that keep churning out of VC land.